Dave MacLachlan: By examining the code (ADC registration required) that implements objc_sync_enter and obc_sync_exit, we can see that on every @synchronized(foo) block, we are actually paying for 3 lock/unlock sequences. objc_sync_enter calls id2data, which is responsible for getting the lock associated with foo, and then locks it. objc_sync_exit also calls id2data to get the lock … Continue reading @synchronized